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Dec. 10, 2010 -- Oral contraceptives account for just 1% of the estrogen found in our drinking water supply, according to a new report in Environmental Science & Technology.

Reports of intersex fish, including male fish with some female characteristics, led to widespread concerns about female hormones leaching into the nation’s water supply. Some suspected that estrogen from birth control pills excreted in urine may be a significant contributor, but the new study exonerates birth control pills as a main source of estrogen in our drinking supply. Instead, agricultural sources such as livestock waste, soy and dairy foods, and other pharmaceuticals are among the main culprits.

“When you take a birth control pill, whatever is excreted goes through a treatment plant, so only a very minimal amount reaches the drinking water,” says study author Tracey Woodruff, PhD, MPH, an associate professor and director of University of California-San Francisco's Program on Reproductive Health and the Environment. Unlike human urine, cow urine is not treated before it enters our water supply.

This is not to say that hormones in the drinking water are not contributing to human health problems, including breast cancer, early puberty, and other reproductive issues, she says.

Solutions Needed

“There are a lot of other sources that we should be concerned about,” Woodruff says. Hormone replacement therapy and other drugs also contribute hormones to the drinking supply, she says. But “improvements in drug delivery systems so we use lower doses can help minimize the amount that gets into our water supply."

Woodruff and colleagues analyzed the main sources of estrogen in the drinking water supply. They found that waste water treatment systems remove most of the estrogen found in birth control pills so it never reaches the drinking water. Soy and dairy products and animal waste contribute far more estrogen to the water supply than do oral contraceptives.

What’s more, it’s not just women who excrete hormones in their urine. Men and children excrete hormones in their urine, she says.

Kirsten Moore,president and CEO of the Washington, D.C.-based Reproductive Health Technologies Project, a national nonprofit group advocating for contraceptive and reproductive choices, says “the good news is that estrogen from birth control pills is not the big concern that some media reports have made it out to be.”

“There is reason to be concerned about the estrogenicity of drinking water, but the role that birth control pills play is minimal,” Moore tells WebMD.

Cleaning up the water supply should take priority. “We would like to see more solutions in place like improving water treatments to eliminate some of the sources of estrogen that are making it into the water supply.”

No Evidence Linking Trace Amounts of Estrogen in Water to Health Problems

Jeff Stier, a senior fellow at the National Center for Public Policy Research, a Washington, D.C.-based conservative think tank, points out that this study does not tell us anything about the potential health effects of trace hormones in the water, and that it needs to be viewed through that lens.

“This is not a study that says that traces of estrogen in drinking water causes human reproductive health problems,” he says. “There is no body of scientific evidence which leads to the conclusion that trace levels of hormones in drinking water are a contributor to human health problems, be they from pharmaceuticals or other sources."